Field of the Invention
This invention pertains in general to the field of inhalational anesthesia. More particularly the invention relates to an anesthetic breathing apparatus, and more particularly to a control process in such apparatus for obtaining specific target values of patient breathing gases.
Description of the Prior Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Operators of anesthetic breathing apparatuses previously have spent valuable time adjusting and checking anesthetic breathing parameters, like foremost inspired oxygen and anesthetic agent values, constantly re-adjusting these parameter settings due to changes in uptake and metabolic rate of the anesthetized patient, to ensure safe and effective anesthesia. All this was done by the clinical operator of the apparatus in parallel with a multitude of other time-consuming and complex tasks. Recently anesthetic breathing apparatus are disclosed in which the operator is able to set the target values for these anesthetic breathing parameters and the apparatus automatically adjusts gas delivery to achieve and maintain the set target values. For instance, in United States patent application number US 2009/0050148, an inhalation anesthesia delivery system is disclosed, whereby the system comprises a fresh gas feeding arrangement connected to a breathing circuit, a monitor device, a control device and an interface unit. The fresh gas feeding arrangement and the ventilator are configured to deliver a desired concentration of gas to the breathing circuit, the desired concentration being set by using the interface unit. The monitor device is configured to monitor gas concentrations in the breathing circuit by analyzing gases flowing in the breathing circuit, and the control device is configured to control the fresh gas feeding arrangement on the basis of the data received from the monitor device to keep the desired breathing gas concentration. The monitor device is configured to monitor expired inorganic gas concentration by comparing the measured expired breathing gas concentration with the set target value and changing the fresh gas delivery accordingly to meet the target value.
However, the system disclosed in US 2009/0050148 has limitations, in particular when changing set target values. For instance during induction when ramping up concentration of an anesthetic agent (AA) to a clinically desired target value, the change may be provided in a non-desired way for certain patients. For instance, some brittle patients might be hit by sudden blood pressure drop or other side effects if delivered AA concentration is changed too quickly.
Therefore, inventors have identified the need for an anesthetic breathing apparatus in which the user may choose a desired control path from a current value of at least an AA concentration to a target value of the AA concentration. In this manner, the anesthetic breathing apparatus may be adjusted to obtain a certain AA target value in a clinically advantageous manner. In this manner for instance induction phases, emergence phase, or changes from one AA to another AA or a mixture thereof may be advantageously provided when using automatic control to reach desired clinical target values.
Hence, an improved anesthetic breathing apparatus would be advantageous and in particular allowing for increased flexibility, cost-effectiveness, and/or patient safety would be advantageous.
It is desired that patient safety be improved. An apparatus is desired in which some patients might be anesthetized slower than others, while other, less brittle patients might be anesthetized quicker, in particular in automatic anesthesia modes of the apparatus. Side effects when changing AA values delivered to a patient, like blood pressure drops, are desired to be avoided by such an improved apparatus. Also, during acute situations, like acute caesarian sections, anesthesia is desired to be provided as quickly as possible by such apparatus
Economy of operating an anesthetic breathing apparatus is desired to be improved by such improved apparatus. For instance, a slower ramping up to a desired AA level might be economically more advantageous as expired AA might be more efficiently re-breathed. Wash out of AA and wake-up is desired to be more effectively controlled and predicted. Patient throughput in OR theatres might be increased if for instance predicted times for AA target changes to be effected are provided by the apparatus in a reliable manner. Hence, some improved anesthetic breathing apparatus are desired to provide such estimated times until a set anesthetic target is obtained.